Method of recycling fluorine using an adsorption purification process

ABSTRACT

A method and apparatus is disclosed for producing fluorine by providing a contained fluorine precursor source located proximate to or remotely from an adsorbent bed, optionally in a replaceable unit that may be a replaceable module comprising both the fluorine source and the adsorbent bed. Fluorine derived preferably from a nitrogen trifluoride source and used to remove deposited silicon-containing impurities in reaction chambers is reclaimed from an adsorbent bed, and made available to the reaction chamber as a supplemental fluorine source to reduce the total required amount of nitrogen trifluoride source gas. The separation column adsorbent is regenerated in cyclical intervals using a reverse flow of inert gas.

FIELD OF THE INVENTION

The present application relates to the field of gas purification andrecycling. More specifically, the present invention relates to the useof recycled fluorine to supplement nitrogen trifluoride for cleaningchamber surfaces, and the purification and recycling of fluorine gas.

BACKGROUND OF THE INVENTION

Semiconductor chip manufacturers have long recognized the deleteriouseffects of deposits, such as, for example, oxide deposits on thereaction chamber walls in which the various chemical reactions anddeposition processes take place during chip manufacture. As impuritiesbuild up on reaction chamber surfaces, such as interior chamber walls,the risk increases that such impurities may be co-deposited on targetwork piece surfaces, such as computer chips. Therefore, such chambersmust be periodically cleaned during down cycles in the chipmanufacturing process.

One known way to clean the unwanted deposits from interior reactionchamber walls is to produce a fluorine plasma in the reaction chamber,under sub-atmospheric pressure, to remove unwanted silicon-containingoxide deposits from the interior chamber walls. While diatomic fluorine(F₂) is an excellent candidate as a source for the fluorine plasma, itis highly reactive. Therefore, the fluorine plasma can be more safelyobtained by dissociating other fluorine-containing compounds such as,for example, NF₃, CF₄, C₂F₆, SF₆, etc. In essence, anyfluorine-containing gas that can be decomposed into active fluorinespecies potentially can be used for chamber cleaning.

Nitrogen trifluoride (NF₃) has proven to be an extremely safe, usefuland versatile source of elemental fluorine for reactions, and for use inapparatus cleaning protocols. However, the dramatic surge in demand forNF₃ has resulted in a virtual global shortage of this relativelyexpensive material. In addition, most of the cleaning processes usingNF₃ only consume about 15% of the fluorine contained within the NF₃ inthe actual cleaning operation, with the remaining fluorine beingexhausted, treated, neutralized and eventually discarded.

Cyclical adsorption processes are generally employed for use in fluorinerecycling processes. Such preferred processes include pressure swingadsorption (PSA) and temperature swing adsorption (TSA) cycles, orcombinations thereof. The adsorption can be carried out in anarrangement of two or more adsorption beds arranged in parallel andoperated out of phase, so that at least one bed is undergoing adsorptionwhile another bed is being regenerated. Specific fluorine recycleapplications into which the invention can be incorporated include vacuumvapor deposition and etching chamber cleaning processes, etc.

The fluorine-containing source compound, any other reagents, and inertgases used in the chamber cleaning process are typically supplied ascompressed gases and are admitted into the chamber using a combinationof pressure controllers and mass flow controllers to effect the cleaningprocess. The cleaning process itself requires that a plasma bemaintained upstream of, or in the chamber to break up thefluorine-containing source compound so that active fluorine ions andradicals are present to perform the cleaning chemistry. To maintain theplasma, the chamber is kept at a low pressure, typically between about 1and 10 Torr absolute, by using a vacuum pump to remove the gaseous wasteproducts and any unreacted feed gases that comprise the exhaust gas. Thepressure in the chamber is typically controlled by regulating the flowof exhaust gas from the chamber to the chamber pump using a vacuumthrottle valve and feedback controller to maintain the chamber pressureat he desired setpoint. The chamber cleaning operation is performedintermittently between deposition operations. Typically, one to fivedeposition operations will be performed between every chamber cleaningoperation.

In typical reaction chamber cleaning apparatuses the reaction gases areNF₃ and argon. Typically the NF₃ is dissociated into nitrogen andenergetic fluorine radicals. However, the unused radicals recombine toform fluorine, which is directed from the system as waste and exhausted,such as to a facility abatement device.

It would be advantageous to reclaim a portion of the fluorine waste bypurifying the fluorine, discarding the impurities in the waste streamand then return the fluorine for use in the cycle. However, traditionalpacked column separation techniques have proven unsuitable or unreliablefor use with fluorine. Fluorine's high degree of reactivity andinstability makes a successful adsorbent selection (for use as adsorbentpacking within a separation column) extremely difficult. The adsorbentwill combust, or otherwise adversely react prematurely and unpredictablyunless the materials used to make the column and the adsorbent bed aremade to be non-reactive with fluorine, or are protected by a stablefluoride layer. Traditional steel columns are often too reactive, andplastic vessels and beds combust easily. Silica gels and molecularsieves are also unsuitable for fluorine separation due to their lack ofstability when exposed to fluorine.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a method forrecycling fluorine from a waste stream by providing a process chamberhaving an inner surface, said surface having contaminants and providinga stream of fluorine-containing gas from a flowing gas source into theprocess chamber. The contaminants are contacted with thefluorine-containing gas and removed from the process chamber innersurface to create a waste stream. The waste stream is directed from theprocess chamber to a purification chamber comprising an adsorption bedcontaining an adsorbent that adsorbs contaminants in the waste stream inthe purification chamber. The waste stream is converted into a recycledfluorine source stream and directed from the purification chamber to theprocess chamber as a supplemental fluorine source stream.

In another embodiment, the present invention is directed to a method forcleaning impurities from an inner surface of a reaction chamber byproviding a process chamber having impurities on an interior surface anddirecting a flow of a fluorine-containing compound to the processchamber from a fluorine-containing source. The fluorine from thefluorine-containing compound is dissociated with the fluorineassociating with the impurities on the interior surface of the processchamber. The fluorine is directed along with the associated impuritiesfrom the process chamber to a purification chamber, said cleaningchamber containing an amount of adsorbent onto which the impurities areadsorbed. The purified fluorine is directed from the purificationchamber to the process chamber to supplement the fluorine-containingsource.

In yet another embodiment, the present invention relates to a method foradsorbing impurities from a fluorine-containing stream in an adsorbentbed by directing a flow of a fluorine-containing compound to a processchamber having an inner surface with impurities deposited on the innersurface and dissociating the fluorine from the fluorine-containingcompound, to associate with the impurities in the process chamber. Thefluorine with impurities is directed from the process chamber to apurification chamber that contains an amount of adsorbent for adsorbingthe impurities onto the adsorbent. The purified fluorine is directedfrom the purification chamber to a fluorine storage tank.

In addition, the present invention is directed to an apparatus forcleaning impurities from a reaction chamber having a process chamberhaving at least one inlet and one waste stream outlet, the inlet influid communication with a source of fluorine; a waste stream fordirecting a fluorine-containing compound and impurities from the processchamber in fluid communication with the process chamber; and apurification chamber having an inlet and an outlet, the purificationchamber inlet in fluid communication with the waste stream outlet andpreferably located downstream from the process chamber, the purificationchamber comprising an amount of adsorbent, with the purification chamberoutlet in fluid communication with a pathway for directing purifiedfluorine from the purification chamber to the process chamber.

In a still further embodiment, the present invention is directed to amethod for producing fluorine by providing a contained fluorineprecursor source located proximate to an adsorbent bed in a replaceableunit, an electrolytic cell comprising an electrode, said cell chargedwith an amount of electrolyte and a power supply. Current is directedfrom the power supply to the electrolytic cell and then the fluorineprecursor is directed to the electrolytic cell. An amount of impurefluorine is collected from the electrolyte of the electrolytic cell anddirected to the adsorbent bed where impurities are absorbed from theimpure fluorine on the adsorbent in the adsorbent bed while directingnewly produced, purified fluorine from the adsorbent bed.

In yet another embodiment, the present invention is directed to anapparatus for producing purified fluorine comprising a replaceablemodule, said module comprising a fluorine precursor source and anadsorbent bed chamber having an adsorbent bed. The chamber is locatedproximately to the fluorine precursor source. The chamber and thefluorine precursor source are in communication with an electrolytic cellfor producing fluorine gas.

In still further embodiments, the present invention is directed toincorporating a replaceable module comprising a fluorine precursorsource and an adsorbent chamber for the production of fluorine to bedirected to the aforementioned processing chamber having at least oneinlet and one waste stream.

In one embodiment, the present invention is directed to a chambercleaning process that incorporates in situ, real-time purification andrecycling of fluorine-containing gases, and that results in a diminisheduse of NF₃. The present methods and apparatuses can be used to recyclethe unused active fluorine species regardless of the original reagentchemical used.

In a further embodiment, the present invention is directed to anadsorbent material comprising CF_(x) (wherein x is from about 0.9 toabout 1.2), and polytetrafluoroethylene (PTFE) in a ratio of about 9:1(CF_(x):PTFE). In a further embodiment, an amount of pore-formingmaterial is added to the composition.

In another embodiment, the present invention is directed to a method forrecycling fluorine from a waste stream. A process chamber is providedwith a waste stream in fluid communication with a purification chamber,said waste stream comprising a fluorine-containing mixture containingimpurities. A purification chamber is provided in fluid communicationwith the waste stream. The purification chamber is packed with an amountof CF_(x) adsorbent in a separation zone, wherein x is from about 0.9 toabout 1.2. The waste stream is directed from the process chamber to thepurification chamber, and an amount of fluorine is separated from thefluorine-containing mixture in the purification chamber. The impuritiesin the waste stream are adsorbed on the CF_(x) adsorbent in thepurification chamber, and the purified fluorine is directed from thepurification chamber to a storage tank, or sent directly into theprocess chamber. Efficient adsorption of the impurities to be capturedon the CF_(x) preferably occurs in the temperature range of from about−150° C. to about 20° C., more preferably from about −80° C. to about10° C., and most preferably from about 40° C. to about −10° C. Further,the desired efficient adsorption of the impurities on the CF_(x)preferably occurs in the pressure range of from about 300 torr to about2000 torr, and more preferably from about 500 torr to about 1200 torr.

In still another embodiment, the present invention is directed to amethod for cleaning impurities from an inner surface of a reactionchamber. A reaction chamber, or process chamber is provided havingimpurities on an interior surface, and a flow of a fluorine-containingcompound is directed to the process chamber from a fluorine-containingsource. The fluorine is dissociated from the fluorine-containingcompound, said fluorine associating and reacting with the impurities onthe interior surface of the reaction chamber. The fluorine andimpurities are directed out of the reaction chamber, preferably undervacuum, to a cleaning chamber, said cleaning chamber packed with anamount of CF_(x) adsorbent, wherein x is from about 0.9 to about 1.2,and the CF_(x) comprises an amount of PTFE. The impurities are adsorbedonto the CF_(x) thereby releasing, purified fluorine from the adsorbentbed The purified fluorine is eventually directed from the purificationchamber to the process chamber to supplement the fluorine-containingsource in the process chamber. Efficient adsorption of the impurities tobe captured on the CF_(x) adsorbent preferably occurs in the temperaturerange of from about −150° C. to about 20° C., more preferably from about−80° C. to about 10° C., and most preferably from about −40° C. to about−10° C. Further, the desired efficient adsorption of the impurities onthe CF_(x) preferably occurs in the pressure range of from about 300torr to about 2000 torr, and more preferably from about 500 torr toabout 1200 torr.

Further, the present invention is directed to a method for adsorbingimpurities from a fluorine-containing stream in a regenerated adsorbentbed. A flow of fluorine-containing compounds from a fluorine-containingsource is directed to a process or reaction chamber. The fluorine isdissociated from the fluorine-containing compound. The fluorineassociates and reacts with the impurities in the processing chamber, forexample, on the interior surface of the processing chamber. Thefluorine, commingled with impurities, is directed to a purificationchamber containing an amount of CF_(x) adsorbent, wherein x is fromabout 0.9 to about 1.2 and the CF_(x) comprises an amount of PTFE. Theimpurities are adsorbed onto the CF_(x) and the liberated, purifiedfluorine is directed from the purification chamber to a fluorine storagetank. To accelerate regeneration of the CF_(x) adsorbent bed in thepurification chamber during off-cycle (when the process chamber is notbeing cleaned), a flow of inert gas is preferably directed through aninlet into the cleaning chamber, and the adsorbed impurities and inertcompounds are removed from the CF_(x) and exhausted from thepurification chamber.

Still further, the present invention is directed to an apparatus forcleaning impurities from a process chamber having at least one inlet andone waste stream. The process chamber inlet is in fluid communicationwith a source of fluorine. A waste stream for directing afluorine-containing compound and impurities from the process chamber areboth in fluid communication with the process chamber and a purificationchamber. The purification chamber has an inlet and an outlet, the inletbeing in fluid communication with the waste stream, and locateddownstream from the process chamber. The purification chamber comprisesan amount of CF_(x) combined with an amount of PTFE, preferably in a wt% ratio of about 9:1 (CF_(x):PTFE) as an adsorbent for the impurities,wherein x is from about 0.9 to about 1.2, with the purification chambercolumn outlet in fluid communication with a pathway for directingpurified fluorine from the purification chamber to the process chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a block diagram describing a typical reaction chamber cleaningprocess.

FIG. 2 is a schematic representation of a preferred process of thepresent invention; and

FIG. 3 is a graph showing the reaction cycle of a representative processof the present invention.

FIGS. 4 and 5 are schematic representations of a preferred embodiment ofthe present invention showing a modular HF source and adsorbent bed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

FIG. 1. is a simple drawing showing a typical reaction chamber cleaningapparatus. Block A represents a source manifold for the chamber cleaninggases. In a typical configuration the gases used are NF₃ and argon.Block B represents a remote plasma generator. Block C is a pressurereading instrument. Block D represents the reaction chamber from whichunwanted deposition products are to be cleaned. Block E is a largethroat vacuum valve and vacuum pump, which together with Block Cprovides pressure control during the reaction clamber clean cycle. BlockF is an exhaust port leading to an abatement device.

During a typical chamber cleaning process, a flow of argon in the rangeof from about 1 to about 6 slm from the source manifold (A) isestablished and allowed to flow into the remote plasma generator (B).Pressure in the generator is kept between from about 1 to 4 Torr by afeedback loop established between the pressure reading instrument (C)and the large throat vacuum valve and vacuum pump (E). A plasma isignited and allowed to stabilize. A flow of NF₃ from (A) is thenestablished usually in the range of from about 1 to about 6 slm. Theargon flow is adjusted to meet process requirements usually in the rangezero to two times the NF₃ flow rate. Once the flow rates havestabilized, pressure in the generator is maintained in the range of fromabout 1 to about 10 Torr.

In the remote plasma generator (B), the NF₃ is dissociated into nitrogenand energetic fluorine radicals. The outlet flow from the remote plasmagenerator then comprises a gas mixture containing amounts of fluorineradicals, nitrogen, argon and undissociated NF₃. This gas mixture entersthe reaction chamber (D). In the reaction chamber (D) the energeticfluorine radicals react with unwanted deposition products, such assilicon-containing oxides, etc. thereby cleaning the chamber of unwanteddeposits. This reaction proceeds typically for a period of from aboutone to several minutes until the unwanted deposition products areremoved from the chamber. In some cases, the reaction endpoint ismonitored with an optical endpoint indicator.

During chamber cleaning only a small fraction of the available fluorineradicals react to remove the unwanted deposition products from thereaction chamber. Indeed, the majority of the fluorine radicalsrecombine to create elemental fluorine. This fluorine is not availableto participate in further cleaning reactions. Instead, this fluorinealong with nitrogen, argon, undissociated NF₃, SiF₄, oxygen and otherreaction products is exhausted to a facility abatement device (F)through the large throat vacuum valve and vacuum pump (E).

FIG. 2 shows one preferred embodiment of the present invention. As shownin FIG. 2, in one embodiment, the present invention is directed to astand-alone recycle-based cleaning support system 10 comprising cleaningchamber 12 in fluid communication with a generic process chamber 14.This recycling system delivers recycled fluorine gas from the cleaningchamber to the process chamber. The cleaning gas comprises variableamounts of NF₃, CF₄, recycled F₂, F₂ from other sources, other fluorinecontaining gases, such as SF₆, and variable amounts of inert gas such ashelium or argon. The recycle system removes exhaust gas from the processchamber 14 which is typically under vacuum during cleaning, whilemanaging the abatement and/or recovery, purification, blending, andre-introduction of the cleaning gas into the process chamber 14 toachieve some composition and pressure setpoint in the chamber 14.Ultimately, the recycle system of the present invention manages theavailable resources (tool exhaust waste, supply gases, power) to lowerthe total cost of operating the tool cleaning process.

The process chamber 14 includes the remote plasma generator (not shown).The gas supply 16 and exhaust system 18 used for oxide deposition areshown separate from the cleaning process. Three port switching valve 22selects between the process gas vacuum pump 24 or the recycle pump 26for process chamber exhaust management. Valves 27 and 28 are used toisolate the process gas supply system 16 and process gas vacuum pump 24.Note that valve 27 may actually represent more than one valve.

Valve 30 preferably is a large throat vacuum valve. In some controlcases it can be operated as a throttle valve, in which case a pressuresignal is taken from pressure transducer (not shown) and used to adjustthe opening of valve 30 in a feedback loop to control the total pressurein the process chamber 14. In other control cases, valve 30 is set to apartially open throttling position or simply set to the full open orfull closed position.

Recycle pump 26 preferably is a large displacement vacuum pump that iscompatible with the use of a purified (nearly 100%) fluorine gas stream.The available displacement is designed to deliver the required vacuumlevels in the process chamber 14 during cleaning. In general, the pump26 will require purging with a dry inert gas such as argon, nitrogen andhelium.

Pressure transducer 36 senses pressure (vacuum) on the inlet side 38 ofthe recycle pump 26. Mass flow controller 40 supplies an inert gas usedto purge portions of the recycle pump 26. Pressure transducer 42 sensespressure (vacuum) on the outlet side 44 of the recycle pump 26. Checkvalve 46 controls venting of the recycle pump exhaust 20 to theabatement system (not shown), which is assumed to run at about 1atmosphere absolute. Valve 46 is shown as a check valve allowing flow tothe abatement system whenever the pressure of the recycle pump exhaust20 is above the abatement system pressure, but also preventing backflowfrom the abatement system when the pressure at pressure transducer 42 isless than the abatement system pressure. Valve 46 could also be amechanical backpressure regulator or a throttle valve together with afeedback controller operating with pressure transducer 42 to maintain apressure setpoint.

Valves 52 and 54 control flow of gas from the outlet 44 of the recyclepump 26 to the inlet 56 of the cleaning chamber 12. Preferably, valve 54is a full flow open/close valve and valve 52 is a restricted flowopen/close valve. It is understood that a single throttle valve (notshown) could replace this valve combination. The use of two valvesrestricts the flow of gas into an adsorbent bed 13 in cleaning chamber12 when there is a large pressure difference and provide a “soft start”.The use of the two valves is also wasteful when the outlet 44 of therecycle pump 26 is at atmospheric pressure and the adsorbent bed 13 isunder vacuum at the start of the adsorption cycle. The adsorbent bedcomprises CF_(x) wherein x is from about 0.9 to about 1.2, and ispelletized according to the methods described herein, said CF_(x)further comprising an amount of PTFE and optionally a pore-formingagent.

According to the present invention, valves 60, 62 would be used when theinlet 38 of the recycle pump 26 is at vacuum and the adsorbent bed 13 isunder pressure at the start of the bed regeneration cycle. Valves 60 and62 control the flow of gas from the inlet 56 of the adsorbent bed 12 tothe inlet 38 of the recycle pump 26. Preferably, valve 62 is a full flowopen/close valve and valve 60 is a restricted flow open/close valve. Itis understood that a single throttle valve could replace this valvecombination. The two valves 60, 62 work to restrict the flow of gas intothe recycle pump 26 when there is a large pressure difference andprovide a “soft start”.

Heat exchangers 64, 66 ensure the gas entering the cleaning chamber 12is at the desired adsorbent bed target temperature, preferably about−30° C. Heat exchanger 64 is optional. Pressure transducer 68 sensespressure (vacuum) in the adsorbent bed 13. Since there is no significantpressure drop through the adsorbent bed 13 pressure transducer 68 couldalso be placed elsewhere, such as at the bed inlet 56.

Valve 70 admits nitrogen (or other inert purge gas such as argon orhelium) from a nitrogen source (not shown) during the bed regenerationcycle to provide a reverse “flush”. It is understood that valve 70 couldbe any useful valve such as, for example, a throttle valve, anopen/closed valve in series with a fixed orifice, an adjustable needlevalve, or a small mass flow controller. Valve 72 and mass flowcontroller 74 control return of purified fluorine-containing recycle gas76 to the process chamber 14. In some control approaches, valve 72 is anopen/closed valve and controller 74 both measures and controls flowrate. Under other control approaches, controller 74 provides only flowrate control (no mass flow measurement) and valve 72 is absent. Understill other control approaches, both controller 74 and valve 72 arepresent, but controller 74 only provides flow rate control.

Mass flow controllers 78 and 80 control the feed of source gases 84, 82respectively, from sources that are not shown (exclusive of recyclegases) to the process chamber 14 during the cleaning process cycle.Depending on the detailed process start up requirements, inert gas 84may or may not be required. Generally, the flow rate of one or moresource gases 82, 84 will be reduced as recycle gas 76 is returned to theprocess chamber. Valve 90 isolates the process chamber 14 from thecleaning gas input streams 82, 84 and 76, such as during deposition.Pressure transducer 32 senses pressure (vacuum) inside the processchamber 14, and is used as an input signal for controlling processchamber pressure during the cleaning process cycle. Control is achievedusing a feedback controller to adjust either the vacuum pumping speed(by controlling valve 30 or the recycle pump 26) or the cleaning gasmixture feed rate (by controlling controllers 74, 78, 80) or bycontrolling both the pump 26 and controllers 74, 78, 80.

In the following mode of operation, the present invention makes controlof the feed gas composition and flow rate the primary control objective,and accepting 100% of the available recycled gas 76 as a secondaryobjective. In this mode of operation, pressure in the process chamber iscontrolled by measuring with pressure transducer 32 and using a feedbackloop to control the position of vacuum throttle valve 30. Pressure inthe adsorbent bed 13 initially starts at zero (end of regenerationconditions). At the appropriate time, valve 52 opens to beginpressurizing the bed 13, in the cleaning chamber 12 at a controlledrate. When the pressure measured by pressure transducer 68 is equal totransducer 42, valve 54 is opened. Pressure in the adsorbent bed 13 isthen determined by pressure drop through valve 46. The feed gascomposition and flow rate to the process chamber 14 are controlled bysetting the flow rate on the individual mass flow controllers. Thesemass flow controller setpoints will vary with time. For example,controller 74 starts out at zero and increases as recycle gas 76 becomesavailable. The setpoints for the other mass flow controllers aredecreased based on the flow of recycle gas 76 and based on keepingvacuum throttle valve 30 from opening too far. When the transducer 68has increased above the target adsorption pressure, the recycle gas isavailable. Recycle gas 76 can be withdrawn from the adsorbent bed 13 upto flow rates where transducer 68 drops below some minimum. Excessexhaust gas 20 from the recycle pump 26 that is not purified for recycleis vented to abatement through valve 46. Assuming that the cycle startsfrom a fully regenerated, evacuated, and isolated adsorbent bedcondition, the following steps occur. Preferably, the process chamberpressure control is enabled using transducer 32, feedback loop, andvalve 30. A flow of plasma ignition gas from feed gas 84 is establishedwith argon in the range of from about 1 to 6 slm and the plasma isignited. A flow of NF₃ is established from feed gas 82 in the range offrom about 1 to 6 slm. The flows are allowed to stabilize, then feedgases 82, 84 are adjusted for cleaning conditions in process chamber 14.The appropriate gas composition and pressure is then achieved at outlet44 of recycle pump 26. Valve 52 is opened, followed by opening valve 54.After the appropriate pressure is obtained in the cleaning chamber 12,the pressure transducer 68 is monitored. A controlled flow of recyclegas 76 is sent through controller 74 into process chamber 14 followed byreducing the flow of new fluorine containing cleaning gas 82. Transducer68 is monitored to be certain that controller 74 is not over-drawing thePSA bed production rate. Controllers 78, 80, and 74 are adjusted tocontrol feed gases 84, 82 and 76 respectively until end of the processchamber cleaning cycle. The plasma source is then shut off, as is thefeed gas flow (close valve 90, controllers 74, 78, 80, valve 72),followed by closing close valves 52 and 54. Valve 30 is then closed toisolate the process chamber 14 from the cleaning gas recycle system. Thethree port switching valve 22 is set to select the process vacuum pump24. Valve 28 is then opened to evacuate process chamber 14. Since theprocess chamber cleaning cycle is now complete, the process chamber 14can now be used for deposition, and the adsorbent bed 13 in the chamber12 can now be regenerated concurrently, on-line, while deposition takesplace in process chamber 14. Valve 60 is opened followed by valve 62when transducer value 68 is close enough to transducer value 36 for softstart. Valve 70 is then opened to admit a controlled flow rate of flushgas 71 (nitrogen or other inert gas such as argon or helium) to reverseflush the adsorbent bed 13. Valve 70 is closed and the cleaning chamber12 is evacuated. Valve 60 and 62 are then closed to isolate theadsorbent bed 13 in the cleaning chamber 12.

The following mode of operation makes 100% utilization of the availablerecycle gas as the primary control objective, while the control of thefeed gas composition and flow rate are secondary objectives. In thismode of operation, the process chamber exhaust valve 30 is set to afixed position. Pressure in the process chamber 14 is controlled bymeasuring with transducer 32 and using a feedback loop to control theflow 82 of fresh fluorine containing cleaning gas. The feed gascomposition is controlled by adjusting controller 78 (inert gas flow)and valve 30 to indirectly increase or decrease the gas flow 82setpoint. The pressure in the adsorbent bed 13 initially starts at zero(end of bed regeneration conditions). At the appropriate time, valve 52opens to begin pressurizing the bed 13 at a controlled rate. When thepressure measured by transducer 68 is equal to that shown by transducer42, valve 54 is opened. The pressure in the adsorbent bed 13 continuesto increase. When the pressure setpoint for PSA adsorption is reached asshown at transducer 68, valve 72 is opened and a PID loop is used tocontrol the setpoint on controller 74 (or to control valve position) tomaintain the PSA pressure setpoint. In this way, 100% of the availablerecycle gas is returned as feed to the process chamber 14. The processchamber pressure control loop reduces the flow through controller 80 tocompensate and maintain process chamber 14 pressure. Assuming a startfrom a fully regenerated, evacuated, and isolated adsorbent bedcondition, the following steps occur. Valve 30 is opened to the targetthrottle valve position. A flow of plasma ignition gas is establishedand the plasma is ignited. The process chamber pressure control isenabled using transducer 32, feedback loop, and flow controller 80.Valve 30 is adjusted along with controller 78 for the cleaning mode. Theappropriate gas combination and pressure is achieved at the outlet 44 ofrecycle pump 26. Valves 52 and 54 are opened sequentially. Valve 72 isthen opened and the adsorbent bed pressure control is enabled usingpressure transducer 68, PID loop, and controller 74. When the adsorbentbed pressure reaches the target PSA pressure, 100% of the availablerecycle gas 76 is sent to the process chamber 14. The increased feed gasflow to the process chamber 14 will cause the process chamber pressureto increase, which will reduce the flow rate of new fluorine-containingcleaning gas feed 82 through controller 80. Controller 78 and valve 30are set to the throttle position, and chamber pressure control setpointto control feed gas flow until end of the process chamber cleaningcycle. The plasma generator is then shut off as well as the flow of feedgas. This is accomplished by closing valves 90, 72 and controllers 74,78 and 80. Valves 52 and 54 are then closed. Valve 30 is then closed toisolate the process chamber 14 from the cleaning gas recycle system. Thethree port switching valve 22 is set to select the process vacuum pump24. Valve 28 is then opened to evacuate process chamber 14. The processchamber 14 can now be used for any intended operation, such as, forexample, deposition. At this time the regeneration of adsorbent bed 13desirably occurs. Valves 60 and 62 are opened sequentially when thepressure at transducer 68 is close to the pressure at transducer 36.Valve 70 is then opened to admit a controlled flow rate of flush gas(nitrogen or other inert gas such as argon or helium) 71 from a source(not shown) to reverse flush the adsorbent bed 13. Valve 70 is thenclosed and chamber 12 is evacuated. Valves 60 and 62 are then closed toisolate the adsorbent bed 13.

FIG. 3 is a graph showing the adsorption cycle of the present invention.The symbol (Δ) represents the SiF₄ concentration at the outlet 58 of theadsorbent bed chamber 12. At the beginning of the cycle underinvestigation, the SiF₄ concentration at the outlet 58 is at somerelatively high level until the operating pressure equal to about 600Torr at about −30° is achieved in the adsorbent bed 13. Once theoperating pressure is reached, the graph shows that, during this phaseof the recycling process, the SiF₄ concentration at the adsorbent bedoutlet 58 drops appreciably as the SiF₄ is adsorbed on the CF_(x)adsorbent in the adsorbent bed 13. As shown in FIG. 3, as the pressurein the adsorbent bed 13 is reduced, the SiF₄ concentration at the outlet58 of the adsorbent bed 13 predictably begins to once again increase tothe relatively high level noted earlier in the cycle. Typical reactionchamber cleaning processes flow NF₃ in the range of from about 1 toabout 2.5 slm and argon in the range of from about 0 to about 5 slm. Theduration of NF₃ chamber cleaning processes is in the range of from about50 to about 300 seconds.

According to FIGS. 4 and 5, a preferred purified fluorine system 98 isprovided. A novel modular, replaceable unit 100 is contemplatedcomprising a fluorine precursor source, preferably hydrogen fluoride(HF) cylinder 102 and an adsorbent bed 104. Preferably the bed 104comprises CF_(x), NaF or combinations thereof. The bed 104 is preferablychilled to capture low levels of contaminants that may arise from theHF, such as SiF₄, AsF₃, AsF₅, etc. The HF cylinder 102 contains thefluorine source precursor that is required for the purified fluorine gasproduction. The HF cylinder 102 is connected to an electrolytic cellchamber 106, preferably containing KF.2(HF) electrolyte 108. A carbonelectrode 110 is placed into the electrolyte 108, and a current from apower supply 109 is applied across the electrode (anode) 110 and theoutside of the cell chamber 106. Fluorine is then generated on the anodesurface 110 and hydrogen is generated on the chamber walls 112. Thehydrogen leaves the system through pathway 114, and is diluted,preferably with nitrogen in a pressure control and dilution tank 116.The fluorine produced contains HF, KF and other impurities, and isdirected to the bed 104 in the replaceable module 100. The HF and otherimpurities are adsorbed by the adsorbent bed 104. The purified fluorineis then directed from the bed 104 to a fluorine surge tank 118 until thefluorine is ready to be directed to the process of FIG. 2 as thefluorine source 82, as shown in FIG. 5. The term “purified fluorine” isunderstood by those skilled in the field of gas manufacture andpurification as being as impurity-free as exposure to the adsorbent bedwill allow, approaching about 100% fluorine. The use of the fluorineproduction system 98 does not generate N₂ and therefore delivers ahigher concentration of fluorine delivered to the chamber 14. This willfurther reduce the high cost of remote plasma chamber cleaning byreducing the total gas flow to the adsorbent bed chamber 13 of process10. In addition, the purified fluorine system 98 can preferablyeliminate the use of NF₃.

FIGS. 4 and 5 further show the modular aspect of the HF cylinder 102 andbed chamber 104, shown as a unit 100 being removable from the purifiedfluorine source system 98. FIG. 5 depicts the purified fluorine supplysystem used in concert with the stand-alone recycle-based cleaningsupport system 10 of FIG. 2.

Preferably, the bed is chilled to about −30° C. to effectively removecontaminants such as SiF₄ from the fluorine being produced. The modulemay be periodically removed when the HF in the HF source is depleted.The HF source may then be refilled, and the bed may be regenerated, suchas by heating from about 150° C. to about 300° C. to remove the adsorbedHF and other contaminants from the system. The HF capacity preferablyranges from about 10 lbs to about 75 lbs.

In one preferred embodiment, the fluorine generation system as shown inFIG. 4 sized and designed in accordance with overall reactor dimensions.Fluorine production rates of 70 grams per hour are made possible with a100 amp electrolytic cell. The product fluorine produced and leaving thefluorine generator would be purified fluorine at from about 0 psig toabout 30 psig.

In one preferred embodiment, the semiconductor cleaning process takingplace in the process chamber operates for about 1.5 minutes, with athree minute deposition time. During this entire 4.5 minute cycle time,the fluorine is allowed to accumulate in the fluorine surge tank. Thepressure in the surge tank will be relieved until the fluorine contentsare consumed and the system begins to consume fluorine being produced bythe fluorine generator.

The module shown in FIGS. 4 and 5 is a safety-rated gas cabinet ratedfor HF and fluorine, and it is contemplated that the module will beappropriately ventilated to meet safety and building codes. The contentsof the HF cylinder will be monitored by a gauge or scale, which willalert the operator to low HF levels. When the HF is depleted, the entiremodule may be removed and sent back to the vendor for bed regenerationand HF refilling or replacement. In this way the end-user receives afreshly regenerated bed and refilled HF cylinder to be replaced in thefluorine point-of-use system.

According to the present invention, the novel process of separating,purifying and recirculating fluorine to reduce the amount of NF₃reactant required in a reaction chamber cleaning process, in a closedsystem, is made possible for the first time due to the use of the novelCF_(x) of the present invention as the bed material in the adsorbentbed. The preferred CF_(x) of the present invention is made such that “x”is about 1 and, more specifically “x” is from about 0.9 to about 1.2,and most preferably “x” is about 1.15. To perform optimally with respectto the present invention, the preferred CF_(x) pellets are manufacturedfrom commercially available CFx powder (Advanced Research Chemicals,Catoosa, OK). More specifically, one preferred adsorbent material foruse in the present invention comprises a composite of 90% CF_(x) and 10%polytetrafluoroethylene (PTFE) in the form of 3 mm×10 mm extrudedpellets. Specific preferred formulations for the CF_(x) of the presentinvention are shown in the examples below. The invention is furtherillustrated by the following examples which. Unless otherwise indicated,parts, percentages and ratios are presented on a weight ratio, or massbasis.

The fluorine-compatible recycle pump used in the process of the presentinvention is unlike most pumps used in the semiconductor industry. Mostrough vacuum pumps are made of cast iron, which is thought to give thebest thermal stability, noise attenuation, strength and materialscapability. Aluminum is inferior in these respects, but is used invacuum pump applications where low weight is important and thecommensurate problems can be discounted. Typically such applicationsinvolve only pumping air or inert gases. However, for applicationsinvolving high levels of fluorine in the gas stream, aluminum hasadvantages, being less reactive to fluorine than cast iron. In addition,aluminum advantageously reacts slowly with fluorine to desirably form analuminum fluoride passivation layer, which prevents or minimizes furtherreaction with the fluorine. This is in strong contrast to typical, knownfluorine applications whereby a stainless steel diaphragm pump would beused, with a relatively high level of inherent vibration and a need todetect leakage through the diaphragm. In the present application, therelatively high flow rates preclude the use of a stainless steeldiaphragm pump.

According to a preferred process of the present invention, the pumpcomprises aluminum impregnated with polytetrafluoroethylene (PTFE). ThePTFE forms a relatively low friction surface to resist galling. In afluorine application, the PTFE coating, which is resistant to fluorineprovides a protective layer to the aluminum. This minimizes the need toslowly passivate the internal surfaces of the pump with fluorine.

In fluorine applications, the use of a single shaft pump isadvantageous. A single shaft pump produces no gear-related noise.Further, the single shaft design provides a low level of well-controlledvibration, which makes it suitable for on-tool mounting. The design ofthe pump eliminates any direct contact rotary shaft seals or flexingdiaphragms to seal the fluorine in the pump. All seals that function tocontain fluorine are static and hence reliable and predictable.

In addition, for fluorine application, the use of a pump with nobearings in the vacuum system is advantageous. The absence of bearingsin the vacuum system results in the separation of lubricants from thefluorine stream. This results in no adverse reaction of the pumplubricant with the fluorine, no contamination of the process chamberfrom the pump lubricant, no contamination of the recycled fluorine gasstream from the pump lubricant and no maintenance requirements of thefluorine-contaminated pump parts.

According to the present invention, the preferred pump apparatus is avacuum pump having pumping speeds of from about 20 m³/h to about 100m³/h and capable of achieving pressures of from about 0.01 mbar to about1000 mbar. Known dry vacuum pump technologies use an inert gas delta Pand close tolerances to limit gas flow to the drive casing. Thesedesigns rely on close geometric clearances to control the pressure dropacross annular clearances around the shaft, and, combined with apressure regulation device, achieve a higher pressure of inert gas thanthat of the drive casing and/or the final stages of the pump with aminimum flow rate of inert gas. According to a preferred embodiment ofthe process of the present invention, this has the advantage ofpreventing fluorine from entering into the pump drive casing andminimizing the dilution of the recycled fluorine gas stream.

As shown in FIG. 2, according to a preferred embodiment of the presentinvention, when NF₃ passes through the process chamber 14 the gases areconverted into fluorine radicals, fluorine gas and nitrogen gas with theratio of N₂ to F₂ being 1:3. Therefore the maximum concentration of F₂is 75%. However this concentration can decrease as the gas becomesdiluted with the required argon/nitrogen purge gases used for thepumping recycle process. Therefore, according to a further embodiment ofthe present invention, according to FIG. 5, concentrations of purifiedF₂ can operate continuously as high as 75%. In this way, the F₂concentration only decreases in the recycle system if the NF₃ feed isused. As stated above, the use of cylinder fluorine is impractical forsafety reasons (the maximum volume that can be placed in such compressedcylinders is 400 psi). Therefore, the fluorine generation system 98 ofthe present invention is useful as such system can supply unlimitedquantities of fluorine on demand with only a reasonable, standard HFcylinder supplying the fluorine gas precursor. The process of thepresent invention as shown in FIGS. 4 and 5 allow the fluorineconcentration to be as high as 100%, if desired, as the gas is passedthrough the recycle pump 26. The fluorine concentration can be alteredas desired from 100% fluorine down to any desired fluorine concentrationby providing the argon/nitrogen gases supplied to the recycle pump 26.Therefore, the present invention as depicted in FIGS. 4 and 5, using thepurified fluorine generation system 98 creates a wide range of flowconditions that will enter the process chamber 14, including conditionsthat would not be possible using NF₃ alone. The flow rate of F₂ enteringthe system preferably ranges from about 1 L/min to about 6 L/min.

EXAMPLE 1

CF_(x) Adsorbent Formation with Pore Formation

a. One preferred CF_(x) component used to make the adsorbent bed pelletsof the present invention is commercially available Carbofluor™ CF_(x),grade 2065, (wherein x is approximately 1.15) which is manufactured as apowder by Advanced Research Chemical (ARC, Catoosa, OK). The PTFEcomponent was Dyneon grade TF™ 2071, and is also manufactured as apowder. The PTFE is believed to act as a binder for the pellets. Inaddition, isopropanol, or FC-84, which is C₇F₁₆ (3M Company,Minneapolis, Minn.) was added to the mixture before extrusion, and wasremoved after extrusion by adding heat or vacuum. It is believed thatthe addition of the isopropanol aids in pore formation. Isopropanol waspreferably added in amounts of 64 ml/100 g combined weight of the othercomponents. The pellets were extruded with an Amandus Kahl L 175laboratory pellet press using an Amandus Kahl (Hamburg, Germany) 3 mmdie with a 9:1 pressway ratio. Table I below shows one recommendedcomposition for the pellets of the present invention. TABLE 1Composition of Adsorbent Pellets Component Component Role QuantityCF_(x), ARC Carbofluor ™, active adsorbent 90 g Grade 2065 PTFE, DyneonTF ™ 2071 Binder 10 g 2-propanol (0.79 g/ml) or Pore former 64 ml 3MFC-84 (1.74 g/ml)

ARC Carbofluor™ Grade 2065 is preferred, but any highly fluorinatedCF_(x) could theoretically be substituted so long as x is approximately1.15 and the compound has a significant adsorption capacity (forexample, a measured N₂ BET surface area of 340 m²/g). Table 2 lists thedesired properties found in ARC 2065. TABLE 2 ARC Carbofluor ™ Grade2065 Properties Color White Carbon Source Carbon Black Total Fluoride64-65% X in CF_(x) ˜1.15 Free oxid. Powder (iodiometric method) <0.2%Median Particle Size <1 μm True Density 2.5 g/ml Bulk Density 0.1 g/mlSurface Area (N₂ BET) 340 m²/g Decomposition Temp 500° C. ThermalConductivity (at STP) ˜0.4 J/m-sec-K Heat Capacity (at STP) ˜0.8 J/g-K**Based on literature value, varies considerably between −200° C. and200° C.

Dyneon TF™ 2071 PTFE is the preferred binder because of its propertiesas set forth in Table 3 below. It is understood that a binder possessingsubstantially similar properties could be substituted for the Dyneon TF™2071. TABLE 3 Dyneon TF ™ 2071 PTFE Median Particle Size 500 μm TrueDensity 2.16 g/ml Bulk Density 0.51 g/ml Surface Area (N2 BET) ˜0 m²/gMelting Point Temp. ˜330° C. Thermal Conductivity (at STP) ˜0.35J/m-sec-K Heat Capacity (at STP) ˜1.4 J/g-K

EXAMPLE 2

CF_(x) Adsorbent Pellet Formation Without Pores

Another preferred adsorbent bed pellet was made using the CF_(x) andPTFE components set forth in Example 1. However, this other preferredadsorbent formed into pellets using the equipment and protocol as setforth in Example 1, did not incorporate the isopropanol and did notrequire pore formation. The CF_(x) used to make the adsorbent bedpellets of the present invention was commercially available Carbofluor™CF_(x), grade 2065, (wherein x is approximately 1.15) which ismanufactured as a powder by Advanced Research Chemical (ARC, Catoosa,OK). The PTFE component was Dyneon grade TF™ 2071, and is alsomanufactured as a powder. The PTFE is believed to act as a binder forthe pellets. The pellets were extruded with an Amandus Kahl L 175laboratory pellet press using an Amandus Kahl 3 mm die with a 9:1(CF_(x):PTFE) pressway ratio. Table I above shows one recommendedcomposition for the pellets of the present invention. Dyneon TF™ 2071PTFE is the preferred binder because of its properties as set forth inTable 3 above. It is understood that a binder possessing substantiallysimilar properties could be substituted for the Dyneon TF™ 2071.

Impurity breakthrough tests with pellets manufactured without apore-forming agent showed low effective impurity capacity and slowimpurity uptake. Impurity breakthrough tests with pellets manufacturedwith a pore-forming agent (Example 1) by adding isopropanol or (NH₄)₂CO₃to the mix before pellet extrusion (with removal by heating) improvedthe effective impurity capacity and rate of impurity uptake, as shown inTable 4. TABLE 4 Effects of Using Pore Former During CF_(x)/PTFEExtrusion CF_(X) 90% 90% 90% 90% Composition ARC2065 ARC2065 ARC2065ARC2065 PTFE 10% 10% 10% DTP 10% Composition DTF2071 DTF2071 2071DTF2065 Pore Former None (0%) 2% 50% IPA 50% IPA (NH4)CO3 Test Temp C.−130 −130 −130 −130 Test Pressure 584 515 515 612 kPa Test 0.79 0.270.27 0.91 Superficial Vel. cm/s Observed 0.025 0.075 0.073 0.065 CF₄capacity g(CF₄)/g(bed)/ kPaCF₄ Observed CF4 74 26 5.7 7.7 EqualizationTime, sec

Based on these results isopropanol (IPA), or 2-propanol is the mostpreferred pore-forming agent. In addition, the use of other organiccompounds, including perfluorocarbon-containing compounds arecontemplated, such as, for example FC-84 (predominantly C₇F₁₆), FC-72(predominantly C₆F₁₄), FC-77 (predominantly C₈F₁₈), FC3283(predominantly C₉F₂₀), and mixtures thereof. The aforementioned FCcompounds are available from the 3M Company, (Minneapolis, Minn.).

According to the present invention, and as shown in the examples, pelletmanufacturing to be used in the adsorbent bed of the present inventioncomprises the following steps: mixing/blending; extrusion; pore formingand drying; smoothing; passivation; and testing. First, the CF_(x), PTFEand pore-forming components are mixed in the desired proportions andblended into a substantially homogenous mixture. This mixture is thenpreferably extruded through a shaping die to form pellets. The pelletsare then dried at 120° C. with an atmospheric flow of dry N₂ for severalhours. The pore former is thus removed from the mixture's matrix,leaving the desired pores. The pellets are then preferably tumbled in avessel to remove rough edges. The pellets may be rinsed and furtherdried with a solvent such as FC-84 (3M, Minneapolis, Minn.) to removedust and residues. Finally, the pellets are passivated to 150° C. in astream of fluorine under atmospheric pressure.

As stated above, known cyclical adsorption processes typically can becarried out using two or more adsorption beds, so that one bed isundergoing adsorption while another bed undergoes regeneration.According to one preferred embodiment of the present invention, only oneadsorption bed is required. This is accomplished by alternating thechamber cleaning step (during which active adsorption occurs) with oneor more deposition steps (where adsorptive bed desorption and bedregeneration occurs). In this way, the bed is regenerated during a cyclewhen the deposition chamber is not being cleaned. Put another way, theprocess chamber cleaning phases and adsorption bed regeneration cyclesare performed out of phase. This preferred single bed arrangement ismore economical from a cost, time and space standpoint than atraditional double bed arrangement.

During the process chamber-cleaning step, the adsorbent bed is in anactive adsorption phase. Exhaust flows from the reaction chamber weredirected through the recycle pump into the adsorbent bed and maycomprise varying amounts of F₂, NF₃, N₂, Ar, SiF₄ and HF. When theoperating pressure of the adsorbent bed is reached, the exhaust flowsfrom the adsorbent bed chamber are directed back to the process chamberminus those impurities, which have adsorbed (i.e. SiF₄, HF) on theCF_(x) adsorbent. The remaining active gases are available toparticipate in further chamber cleaning reactions in the processchamber. This recycling process continues for the duration of theprocess chamber-cleaning step. A significantly reduced amount of freshNF₃ cleaning gas is thus required to clean the process the processchamber clean.

At the conclusion of the chamber-cleaning step and during the depositionstep, the adsorbent bed is regenerated. That is to say, those componentsthat adsorbed during the process chamber cleaning step are desorbed bydirecting a flow of inert purge gas in a direction “reverse” to that ofthe exhaust flows during the chamber-cleaning step through the recyclepump to waste. The flow rate of the inert purge gas is selected togenerate a viscous flow regime in the adsorbent bed. Preferably, priorto the end of the deposition step, the flow of inert purge gas isdiscontinued and the adsorbed bed is evacuated.

Table 5 shows typical operating conditions (pressure, temperature,duration) for the chamber-cleaning step (adsorb mode) and the depositionstep (desorb mode). TABLE 5 Typical Operating Conditions for Adsorb andDesorb Modes Mode of Operating Pressure Operating Duration, Operation(torr) Temp. ° C. (s) Adsorb 500 to 1200 −40 to −10 50 to 300 Desorb 0to 50 −40 to −10 50 to 900

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1-16. (canceled)
 17. A method for cleaning impurities from an innersurface of a reaction chamber comprising the steps of: providing aprocess chamber having impurities on an interior surface; directing aflow of a fluorine-containing compound to the process chamber from afluorine-containing source; dissociating the fluorine from thefluorine-containing compound, said fluorine associating with theimpurities on the interior surface of the process chamber; directing thefluorine and impurities from the process chamber to a purificationchamber, said cleaning chamber containing an amount of adsorbent;adsorbing the impurities onto the adsorbent producing purified fluorine;directing the purified fluorine from the purification chamber to theprocess chamber, said fluorine from the purification chambersupplementing the fluorine-containing source.
 18. The method accordingto claim 17, wherein the fluorine-containing compound comprises nitrogentrifluoride.
 19. The method according to claim 17, wherein the step ofdirecting the fluorine from the purification chamber to the processchamber further comprises directing the fluorine to a storage tank. 20.The method according to claim 17, wherein the impurities comprisesilicon-containing impurities.
 21. The method according to claim 20,wherein the impurities comprise SiF₄. 22-52. (canceled)
 53. A method forcleaning impurities from an inner surface of a process chambercomprising the steps of: providing a process chamber having impuritieson an interior surface; directing a flow of a fluorine-containingcompound to the process chamber from a fluorine-containing source, saidfluorine-containing source at least partially produced by providing acontained fluorine precursor source located proximate to an adsorbentbed in a replaceable unit; providing an electrolytic cell comprising anelectrode, said cell charged with an amount of electrolyte; providing apower supply and directing current from said power supply to theelectrolytic cell; directing the fluorine precursor to the electrolyticcell; collecting an amount of impure fluorine from the electrolyte ofthe electrolytic cell to the adsorbent bed; adsorbing impurities fromthe impure fluorine on adsorbent in the adsorbent bed; and directingpurified fluorine from the adsorbent bed to the process chamber;dissociating the fluorine from the fluorine-containing compound, saidfluorine associating with the impurities on the interior surface of theprocess chamber; directing the fluorine and impurities from the processchamber to a purification chamber, said purification chamber containingan amount of adsorbent; adsorbing the impurities onto the adsorbent;directing the purified fluorine from the purification chamber to theprocess chamber, said fluorine from the purification chambersupplementing the fluorine-containing source.
 54. The method accordingto claim 53, wherein the fluorine-containing compound comprises nitrogentrifluoride.
 55. The method according to claim 53, wherein the step ofdirecting the fluorine from the purification chamber to the processchamber further comprises directing the fluorine to a storage tank. 56.The method according to claim 53, wherein the impurities comprisesilicon-containing impurities. 57-116. (canceled)